Tuberculosis (TB) is a contagious disease that causes 2 million deaths annually. Approximately 9.3 million people worldwide develop TB every year, of which some estimated 4.4 million are undiagnosed. Improving TB diagnostics would result in approximately 625,000 annually adjusted lives saved worldwide, and elimination of TB from industrialized countries. (See, e.g., Center of Disease Control and Prevention, TB elimination: Trends in tuberculosis 2008, (2009); and World Health Organization, Diagnostics for tuberculosis: global demand and market potential. (2006), the disclosures of each of which are incorporated herein by reference.)
White all common TB diagnostic devices, except X-ray, rely on sputum sample collection. Typically, three samples—more than 3 mL each—are collected per patient. This procedure is particularly difficult in some patient populations. (See, M. B. Conde, et al., American Journal of Respiratory and Critical Care Medicine, 162:2238-2240, (2000); and O. D. Schoch, et al., American Journal of Respiratory and Critical Care Medicine, 175:80-86, 2006, the disclosures of which are incorporated herein by reference.) For example, in the case of children, special procedures such as sputum induction and gastric aspiration are required; all of which are unpleasant and difficult for both healthcare providers and patients. (World Health Organization, Introduction and diagnosis of tuberculosis in children. International Journal of Tuberculosis and Lung Disease, 10(10):10911097, (2006), the disclosure of which is incorporated herein by reference.) In cases where sputum induction is not successful, a procedure known as bronchoalveolar ravage (BALI is performed using fiberoptic bronchoscopy. (N. E. Dunlap, et al., American Journal of Respiratory and Critical. Care Medicine, 161(4):1376-1395, (2000), the disclosure of which is incorporated herein by reference.) The procedure requires a medical doctor and can cause infections if the bronchoscope is not properly disinfected. Moreover, sputum samples are usually contaminated with saliva, which lowers their quality (less M. tuberculosis cells per mL) resulting in low diagnostic sensitivities. (M. Sakundarno, et al., BMC Pulmonary Medicine, 9(1):16, (2009), the disclosure of which is incorporated herein by reference.)
Each TB diagnostic test is characterized by its practicality and performance. (See, e.g., World Health Organization, Diagnostics for tuberculosis: global demand and market potential. (2006); World Health Organization, International Journal of Tuberculosis and Lung Disease, 10(10):10911097, (2006); and World Health Organization, Global tuberculosis control: Surveillance, planning, financing (2009), the disclosures of each of which are incorporated herein by reference.) Practicality refers to the time, training, resources, accessibility and cost of conducting the test. Performance refers to the sensitivity and specificity of the test. While an ideal diagnostic would be practical with high performance, current TB diagnostics inherently have a trade-off between the two. (See, WHO citations above.) These diagnostics include: radiographic methods, bacteriological culture, drug susceptibility testing culture (DST), sputum smear microscopy (SSM), and nucleic acid amplification test (NAAT). (See, WHO citations above; and M. D. Perkins and J. Cunningham, The Journal of Infectious Diseases, 196(Suppl 1):S15-27, (2007), the disclosure of which is incorporated herein by reference.) Radiology (chest X-rays) is one of the fastest diagnostics (<1 hr), but suffers from non-specificity and requires expensive equipment operated in a lab. Bacterial culture is considered the gold standard with 87% sensitivity and can detect as low as 10-100 cells/mL from sputum. Further processing of bacterial culture using DST allows the identification of specific strains of MDR-TB. However, obtaining results takes 2-6 weeks in a resource-intensive tab setting. (See, G. E. Pfyffer, et al., Journal of Clinical Microbiology, 35(9):2229-2234, (1997), the disclosure of which is incorporated herein by reference.) SSM is the most practical and widely used test because it is relatively inexpensive and simple. A sputum sample is stained for acid-fastness of M. tuberculosis. More than 10,000 cells/mL of sputum are needed for a positive identification by a microscope operator (ss+). (See, WHO, (2006) publication, cited above.) Because of backlog, these tests can take up to 6 months in some countries and require multiple visits. The SSM sensitivity is less than 60% (as low as 20% in high-risk groups) and although the specificity is high in high-prevalence groups it suffers in industrialized countries. (See, M. D. Perkins & J. Cunningham, cited above.) NAAT has a sensitivity >95% for SSM positive patients (ss+) (60-70% for ss−) with high specificity. 10-1000 cells/mL of sputum contain enough DNA to amplify, hybridize and produce a positive signal. (See, M. D. Perkins & J. Cunningham, cited above.) NAAT and bacterial culture have the highest performance and are the only two tests that can detect MDR-TB. NAAT suffers from low practicality due to sputum-based sample preparation by a lab technician and is therefore highly variable in resource-limited labs. (See, M. D. Perkins & J. Cunningham, cited above.) NAAT would satisfy priorities of developing and industrialized countries if sample preparation methods were cost-effectively automated.
Another diagnostic issue that is challenging the medical community involves hospital-acquired infections (HAIs). According to the Centers for Disease Control and Prevention (CDC), 1.7 million (9.3 per 1,000 patient-days or 4.5 per 100 admissions) annual HAIs occur in U.S. hospitals causing some 99,000 deaths a year. (See, e.g., R. M. Klevens, at al., Public Health Reports, 122, (2007), the disclosure of which is incorporated herein by reference.) In turn, it is estimated that HAIs correspond to annual medical costs exceeding $35 billion. (See, R. D Scott II, Centers for Disease Control and Prevention, 2009, the disclosure of which is incorporated herein by reference.) More and more it is being recognized that HAIs are a serious problem, both from a public health standpoint, and from the perspective of cost-containment for medical expenses.
There are three different routes of transmission for these diseases: touch, droplet, and airborne. Both droplet and airborne transmissions require the formation of an aerosol that can be inhaled to cause infections. For example, one of the most common inhaled infections is pneumonia. Moreover, while hospital acquired pneumonia (HAP) accounts for 11-15% of all HAIs, it causes a disproportionate 36% of deaths. Indeed, some 79% of HAP infections are non-device related and more than 80% are bacterial. (See, D. J. Weber, et al., Infection Control and Hospital Epidemiology, 28(12):1361-1366, (2007), the disclosure of which is incorporated herein by reference.) From this it can be estimated that nearly 160,000 HAIs and 23,000 deaths are caused by inhalation of aerosol bacteria (specifically S. pneumoniae). Furthermore, TB, and multidrug-resistant tuberculosis (MDR-TB) have also surfaced causing further problems in aerosol transmission in hospitals. (See, S. K. Sharma and A. Mohan, Chest, 130(1):261-272, (2006), the disclosure of which is incorporated herein by reference.)
Bacterial aerosol collectors/analyzers that can diagnose contaminants, either directly from a patient or in the atmosphere, have the potential to provide warnings of these infectious agents, and, thereby avoid further infection. However, a key challenge to providing a detector system with sufficient sensitivity is to collect and rapidly amplify the low-concentrations of bacterial aerosol by delivering highly concentrated analyte (such as DNA) to sensors. Conventional sensors simply do not meet the requirements needed to provide direct diagnostic of possible infection or contamination risks from aerosol sources, such as a patient's breath, cough or sneeze, or from the environment. Accordingly, a need exists to provide a bacterial and or biological collector/analyzer for detecting possible sources of infection directly from a patient and/or contamination from airborne bacterial sources.